WiFi is the marketing name for IEEE standard 802.11. It is a standard for both Level 1 (physical) and Level 2 (data link) of a wireless data transmission protocol.

802.11 defines many Level 1 variants. 802.11g is the new, high-speed Level 1 standard, versus 802.11b, the first generation WiFi. The radio frequency band is around 3 Gigahertz, same as a microwave oven. As you can see in your WiFi setup, there are channels within the band. These channels overlap so that at most 3 channels can be in use at the same time.